Insights into the Three-Component Coupling Reactions of Aldehydes, Alkynes, and Amines Catalyzed by N-heterocyclic Carbene Silver: A DFT Study

Abstract

Density functional theory (DFT) was used to investigate the three-component coupling reactions of aldehydes, alkynes, and amines (A3 coupling) using N-heterocyclic carbene silver as the catalyst. This study reveals that the addition reaction between the catalyst N-heterocyclic carbene silver and phenylacetylene (PAE) forms Ag_PAE. Subsequently, one hydrogen atom of the Ag_PAE migrates to the nitrogen atom of the Amine. Thereafter, the amine aldehyde condensation reaction generates a molecule of water and an imine ion with (Path one) or without (Path two) another amine catalyst. Path one has a lower reaction barrier than Path two. Subsequently, the imine ion reacts with silver phenylacetylide to generate the A3 coupling reaction product propargylamine (PPA). Furthermore, the triple bond and −N3 group in PPA undergo a cycloaddition reaction and generate the final product (PR). The entire reaction is strongly exothermic, and, therefore, the reaction is easy to conduct. Moreover, conceptual density functional theory calculations confirm the reaction mechanism. Investigating the mechanism of these reactions will be helpful for understanding and developing new synthesis strategies for similar functional compounds.